1. Field of the Invention
The present invention relate to methods for diagnosing functional long illnesses, particularly with the use of images of the lungs of a subject obtained with a medical imaging modality.
2. Description of the Prior Art
For the diagnosis and therapy of lung illnesses it is necessary to record spatially resolved and time-resolved functional parameters of the lungs using measurement technology. In healthy people the lung is nearly homogeneous, meaning that macroscopically the lung is uniformly filled with fresh air upon inhalation and uniformly emptied upon exhalation. The very thin lung tissue is permeated by a few large and many small blood vessels and bronchi. In a series of different illnesses of the lung, specific areas do not participate in the exchange with fresh air. Such areas can, for example, be filled with mucus, for example in the case pneumonia lung inflammation. Such areas can already be detected in part with conventional x-ray and MR methods.
In the case of certain other illnesses, however, parts of the lung are filled with air without an exchange with the fresh inhaled air ensuing, or the exchange is at least hindered. With asthma, a narrowing of the air passages leads to an at least delayed, but mostly insufficient exhalation of the air. This leads not only to a correspondingly reduced capacity of the lung but also over longer periods of time to a permanent damage of the lung tissue (emphysema). The most frequent causes for this in young patients are asthmatic illnesses or allergies and metabolic illnesses (cystic fibrosis) and others which lead to a local restriction or even collapse of the air passages and, over the long term, to a deterioration of the lung.
In order to be able to detect such functional lung illnesses, among other things it is known to introduce hyper-polarized gases into the lung as a contrast agent. These gases exhibit a nuclear spin and are polarized in a static magnetic field with irradiation of the patient during inhalation. The concentration of the hyper-polarized atoms can then be detected in the MR scanner. Unfortunately, the suitable isotopes are very rare or extremely difficult to provide (for example He3 forms only 0.01% of naturally-occurring helium and, due to its low density, escapes forever after the release into the atmosphere). Alternative isotopes provide only a relatively low contrast due to the low resonance frequency and the poor degree of hyper-polarization. This is the case, for example, for Xe129 with a frequency of approximately ¼ the proton frequency and a hyper-polarization degree of only maximally 10%, compared to approximately 60% for He3. Moreover, the apparatus expenditure in the MR scanner given the use of hyper-polarized gases is not in consequential. Due to the low resonance frequency relative to protons, a dedicated RF system is required, which incurs additional costs. Moreover, an HPG MR measurement can be repeated only in a limited manner since these gases supply no contribution to the oxygen saturation and therefore can be tolerated to a limited degree in patients, in particular those with limited lung function. Alternatively, an examination with radioactive gases (lung scintigraphy) is possible.